The overall objectives are to develop criteria for characterization metal sites in various metalloproteins using variable-temperature magnetic susceptibility, electron paramagnetic resonance, Fe 57 Mossbauer, infrared, electronic absorption, and X-ray photoelectron spectroscopies. In addition to "model" systems, metalloproteins of direct or indirect interest include mushroom tyrosinase, ferredoxins that are potentially mixed-valence such as reduced putidaredoxin, spin equilibria systems such as various cytochromes, P 450 and chloroperoxidase, and various electron transfer systems, particularily cytochrome-C. In an effort to understand the factors determining whether a given system is mixed-valence or not, the thermal electron "intervalence" transfer rates are being gauged for a series of singly-oxidized biferrocene-like molecules where the molecular architecture can be systematically varied. It is proposed that the level of exchange-type interaction is important, and as such J, the exchange parameter in H equals 2JS2.S2, is being determined for the corresponding di-oxidized biferrocenes. Mixed valence work is anticipated on other systems such as the Fe(III)Fe(IV) species obtainable from mono-oxidation of the mu-oxo dimer of ferric tetraphenylporphin. A series of spin-equilibria ferric tris (dithiocarbamates) are being studied with susceptibility (4.2-300 degrees K), epr (4.2-77 degrees K) and variable-temperature (20-300 degrees K) infrared spectroscopy. Attempts are to be made to relate the parameters characterizing the electronic structure of these spin crossover systems to the rates of spin flipping seen for the molecules. Lyophilized samples of mushroom tyrosinase are being studied with variable-temperature magnetic susceptibility.